1. Field of the Invention
The present invention relates to a semiconductor device having a circuit comprising thin film transistor (hereinafter referred to as TFT). For example, it relates to structures of an electro-optical device which is typified of a liquid crystal display device or an EL display device and electric equipment which uses a semiconductor circuit and an electro-optical device or a semiconductor circuit of the present invention.
Note that through this specification, a semiconductor device indicates devices in general which may function by making use of semiconductor characteristics, and that electro-optical devices, semiconductor circuits, and electric equipments are all semiconductor devices.
2. Description of the Related Art
A thin film transistor (hereinafter referred to as TFT) can be formed on a transparent substrate, so that the development of applications to active matrix type liquid crystal displays (hereinafter referred to as AM-LCD) has been actively progressing. High mobility can be obtained in a TFT using a crystalline semiconductor film (typically polysilicon), so that it is possible to realize a high definition image display which integrates function circuits on the same substrate.
Basically in an AM-LCD, a pixel section which displays an image (also called a pixel matrix circuit), a gate driver circuit which drives TFT of each of the pixels arranged in the pixel section, and a source driver circuit, or a data driver circuit, which sends an image signal to each of the TFTs are formed on the same substrate.
In addition to the pixel section and driver circuits, in recent years a system-on-panel has been proposed, in which signal processing circuits such as a signal dividing circuit, a γ compensation circuit, etc., are also formed on the same substrate.
However, it is difficult to satisfy all of the circuit specifications with TFTs having the same structure because the performance demanded by the circuits differs between the pixel section and the driver circuits. In other words, at present a TFT structure has not been established which will satisfy both a driver circuit, which places greater importance on high speed operation, and a pixel section, which places greater importance on high voltage resistance characteristics, at the same time.
The applicant of the present invention has already filed a constitution in which the gate insulating film thickness is made different for a TFT which structures a driver circuit (hereinafter referred to as driver TFT) and for a pixel TFT (see Japanese Patent Application Laid-Open No. Hei 10-056184 and the corresponding U.S. patent application Ser. No. 08/862,895). Specifically, the gate insulating film of the driver TFT is made thinner than the gate insulating film of the pixel TFT.